Steam power plant



Dec. 24, 1957. F. W. RIEHL 2,817,321

STEAM POWER PLANT Filed Feb. 10, 1951 3 Sheets-Sheet 1 Turbine WATER V i1 YNVENTOR. Ffederick W. Riehl BY FIGQ-l ATTORNEY Dec. 24, 1957 F. w. RIEIHL STEAM POWER PLANT s Shets-Sheet 2 Filed Feb. 10, 1951 INVENTOR.

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INVENTOR. Frederick W. Riehl AT T O R N E Y United States Patent F STEAM POWER PLANT Frederick William Riehl, Denver, Colo.

Application February 10, 1951, Serial No. 210,417

19 Claims. (Cl. 122338) This invention relates to a more efficient and effective design for boiler installations in which the major boiler components are pyramided within a cylindrical structure which in addition to being the boiler enclosing shell is also the draft stack for the boiler itself. More particularly this invention pertains and relates directly to a combined boilerstack arranged so a single structure may serve the triple purposes of steam generator, combustion draft producer and exhaust gas conveyor.

Previously, a number of different designs have been developed in an attempt to improve the efficiency of boiler installations having high steaming capacity. In general, these prior developments have been centered around boiler designs, the basic features of which have been known for a considerable number of years. In recent years, improvements adding to the efficiency or capacity of the basic design have materially added to the complexity and inherent congestion coincident with the basic arrangement of all the various boiler elements now possible.

As a result of prior extensive developments, todays steam producing units have a high relative efficiency, and in general they serve the power industry well. However, steam generating units of the present type are so cluttered with steam tubes, drums, super heaters, pre-heaters, draft devices, etc., that the expense of making repairs or improvements in large installations is very high. Further, boilers of the present type together with all necessary auxiliaries take up a considerable amount of plant space that is expensive to erect and maintain.

By contrast, while the steam producing units themselves have become infinitely more complex, the basic design for exhaust gas stacks has of course remained practically unchanged. The efficient smoke stack of today is in most respects the counter-part of the efficient stack of several decades ago. While different types of draft inducing and control devices have been advantageously incorporated, the boiler stack of today is essentially the same tall, centrally open, structure known for several centuries.

With full knowledge of the problems confronting the present day steam production industry, the present inventor has designed a steam generating unit in which all of the basic elements of the modern day steam power plant are incorporated within the interior of a draft stack in such manner that each of the basic elements of the steam producing unit become more efiicient to fabricate, install and service. Besides the advantages inherent in the more convenient placing of the basic boiler elements, the present design also utilizes the formerly open or empty space within the draft stack to the end that the cost of the entire steam producing plant is materially reduced.

The advantages and features set forth above have been the objectives of the inventor in his development of his more eflicient plant. In addition to these objects, the present inventor has intended to provide additional improvements in the various basic boiler elements that will make such elements more efficient, less costly, and easier tp install without the need for separate foundation sup Patented Dec. 24, 1957 ports. Accordingly, it has been the inventors object to provide a novel arrangement for steam tubes, screen tubes and super heaters. Another object has been to arrange the separate basic boiler elements in such manner that the flow pattern of gases and fluids therethrough will be highly efiicient to the end that a minimum of power must be expended to compensate for losses in flow efliciency. Still further objects and advantages of the present invention will be apparent from the appended description and drawings in which:

Fig. 1 is a side elevation in quarter section showing the relative placement and proportionate size of the various boiler elements.

Fig. 2 is a sectional elevation showing in greater detail the features of the lower portion of the inventors steam generating unit.

Fig. 3 is a cross sectional plan view taken along the line 3-3 of Fig. 1.

Fig. 4 is a cross sectional view taken along the line 44 of Fig. 1 showing the arrangement of the super heater tubes.

Fig. 5 is an elevational view showing the features of a separate super heater element.

Fig. 6 is a cross sectional view taken along the line 6-6 in Fig. 5.

Fig. 7 is a cross sectional plan view taken substantially upon the line 77 of Fig. 2 showing additional features of the present invention.

Briefly stated the present invention provides a vertical cylindrical structure which serves the dual purpose of being at one time both the boiler and stack units of a steam generating plant. The combustion gases pass up vertically through the center of the cylindrical structure largely without interference in a single flow direction which assures maximum contact between the heated gases and the steam producing units of the boiler. Because of the unidirectional flow pattern, the boiler arrangement of this invention is largely free of gas pockets or areas of structurally damaging heat concentrations. The steam generating units inclusive of the steam tubes, super heaters, re-heaters and the like are arranged in mutually cooperative positions within the cylindrical structure so that any of the separate elements may be easily removed from the boiler without necessitating removal of other elements. In addition the boiler elements are positioned to protect each of the elements from excessive heat while assuring maximum contact for high output efiiciency.

The necessary boiler auxiliaries are arranged within the cylindrical shell of the combined Boiler-Stack so that upwardly passing heated gases are efficiently used without change in flow direction to pre-heat the water being introduced in the steam drums and steam tubes as well as to pre-heat the air used by the burner units. As the gases pass on upwardly out of these pre-heat units, they are allowed to flow through a dust collector before being released through the open upper end of the stack or before being accelerated by an induced draft fan.

Besides materially increasing the efficiency, serviceability and utility of steam generating units, the invention herein described reduces the total area that must be' devoted to steam production facilities as well as reducing the overall cost of installation. Since only a single foundation must be provided and further since the already necessary structure of the boiler stack is utilized to enclose the steam generating units, the monetary savings, possible through use of this design are remarkably substantial.

General structural arrangement.

Referring now to the drawings, it will be noted in Figs. 1 and 2 that the steam generating unit G of this invention is separated along its vertical extent into a lower halt 2,817,321 i i I constituting a steam producing section S comprising the portion shown in Fig. 2 and an upper half constituting an auxiliary section and upper stack portion. Actually the steam generating section S shown in Fig. 2 includes other auxiliaries such as the burners B and the ash disposal pit and service section P. Located in the stack above the steam-producing section S is a feed water pro-heater W; an air pro-heater H is positioned above the water preheater W, and a dust collecting section C is positioned above the air pre-heater H.

After passage of the furnace gases through the steam generating section S they pass through the auxiliary section for discharge out of the open end of the structural shell or selectively into the intake of a centrifugal or other type of exhaust fan for discharge into the atmosphere at an elevation closely corresponding to the height of present boiler stacks for installations of equal capacity. Besides creating a natural draft through the steam generating unit G, the vertically elongated arrangement of the steam generator makes it possible to discharge the furnace gases at a sufiicient elevation so the gases will not be noxious to the surrounding community.

Preferably the steam generating unit G of this inven tion is made up of an elongated cylindrical shell erected in a vertical position above a foundation 16 and with substantially its entire end surface engaging the foundation. Since the characteristic arrangement desired and shown in the accompanying figures is intended for use in steam generating units having a relatively high output capacity comparable with the power plant boilers of the present day, the shell 15 will usually be made up out of pre-formed steel sheet material that is riveted. welded or otherwise joined together to form an upright cylindrical shell having a height of at least 100 feet. Because of the cylindrical cross-section of the shell 15, the fabricated structure will be relatively strong thereby eliminating the necessity for external or internal frame members and cross bracing. In fact when sheet material of proper thickness is used for any particular installations, all of the separate boiler auxiliaries and steam generating units used may be supported by the cylindrical shell alone. This represents a considerable structural advantage over present types of boilers where it is often necessary to provide for structural frame members to support the various boiler auxiliaries.

A further structural advantage inherent in the present design that will substantially reduce the erection cost of a steam power plant is the fact that the foundation 16 provided for the steam generating unit G of this invention does not have to be as large or contain as much material as the foundations now necessary for separate boiler and stack units. In fact, it is possible that the foundation for a steam generating unit G as described may even be smaller than the foundation necessary to support just the stack unit of prior installations. This is true because the placing of boiler and auxiliary units within the shell 15 tends to materially increase the weight of the stack itself. As the weight of the structure is increased, the effects of wind loads acting against the up right structure and reflected upon the foundation are reduced. Since the massive foundation structures on common types of boiler stacks are in large part necessitated by wind loading factors, any reduction in the effectiveness of wind loads would materially reduce the size of the foundations needed for this type of upright structure.

Through the greatest portion of its vertical extent, the shell 15 is protected from heat and furnace gases by insulation material 17. Preferably the material used should be a fill type insulation, however, where it is deemed necessary, brick work or other solid insulation may be provided.

In addition to the mounting flanges, brackets and the like which will be necessarily attached to both the inner and outer surfaces of the shell 15, stairways l8, catwalks, ladders 19 and platforms 21 can be afiixed to the exterior surfaces of the shell 15 at desired positions for facilitating the observation and servicing of the various boiler elements.

Spaced access openings should be provided in the shell adjacent to the various boiler elements so that tubing and other structural members may be conveniently removed, repaired or serviced. In addition to such miscellaneous openings, the boiler shell may be provided with a door 22 in the lower ash disposal and servicing section P. Since this section is insulated from the steam generating section S by additional insulation 17, workmen may enter the door 22 to accomplish necessary operations in the ash pit 23 or to adjust the blowdown valves 24 in the blowdown discharge pipe 26 which discharges directly into the blowdown piping 25. For most installations it will be desirable to place the ash pit disposal and service section P below the main floor level of the power plant, accordingly as shown in Fig. l, the turbine floor 27 will be on a convenient level for the servicing of the burners section B. Because of the relatively close positioning possible, the amount of piping between the boiler or steam generating unit G and the turbine itself may be kept to a minimum. Further, it will be possible in this type of installation for the turbine operator to adjust and service the burners B.

Burners Since powdered coal is the basic fuel for steam power plant usage at the present time, the present embodiment of this invention is shown as being equipped to burn powdered fuel although other fuels may be used in this design when desired. In such an installation, the controlled pre-heated air coursing downwardly through the trunk conduit 37 is introduced into a header 38 of circular cross section disposed in an encircling position about the shell 15 of the steam generator G. At spaced positions about the header 38, outlet nozzles 39 are jointed to the header 38 so that the heated air from the header may be introduced into the interior of the boiler shell. Preferably, these outlets 39 are positioned so that the air and fuel emitting therefrom will blast in an upward and approximately tangential direction into the interior of the furnace. The flow of air and fuel through each of the separate nozzles 39 is preferably controlled by valves 41 that may either be manually or automatically operated. The powdered fuel is introduced through the nozzles 39 by means of a delivery pipe 42 interconnecting coal pulverizing mechanism (not shown) to the header 38 adjacent to each of the burners 39. Actually the supply pipe 42 extends through the header 38 and through a portion of the nozzles 39 so the powdered coal is mixed with the pro-heated air adjacent to the outer end of the outlet nozzles 39. The upward and tangential direction of the nozzles is utilized to create an upwardly swirling flow of combustion products. The upwardly directed component of such swirling flow tends to materially increase the velocity of flow through the steam generating unit G while the rotating movement of the flow pattern tends to assure equal and etficient contact between the heated gases and the steam producing elements within the steam generator G. The flow pattern described when used in conjunction with the vertically aligned arrangement of other elements shown creates a draft directed upwardly through the generator G of mag nitude greater than the draft through ordinary stacks. In fact, because of the low draft loss characteristics in herent in the aligned placement of boiler elements and because of the very high initial draft created by the extreme temperatures adjacent the burners B at the base of the shell 15 installations of this type may usually be operated without the efficiency decreasing use of power for fan purposes.

In their passage upwardly from the burners .39, the heated gases come first into contact with the steam producing elements of the steam section S. Here the gases give up a considerable portion of their heat, however, there is still a considerable amount of recoverable heat content in such gases as they flow out of the steam producing section upwardly into the auxiliary and upper stack section.

Steam producing section The primary purpose of the steam generator G is of course, the production of steam having a suflicient temperature and pressure to accomplish the desired purposes. The described embodiment of this invention has been intended primarily for the production of steam that could be utilized to run modern types of turbine generators. Accordingly, the steam producing section S of the described embodiment incorporates many features that are especially adapted to the production of steam for turbine operation. However, it will be noted that many of the features used are universally advantageous.

Pro-heated water or steam from the auxiliary section is introduced downwardly through the pipes 52 into a hollow toroidal or circularly formed steam drum 51 positioned close to the top of steam producing section S and supported on the shell by supports 58. Preferably, the water or steam is introduced into the lower portion of the steam drum at a point that would be below the level of water in the drum.

The full circle construction of the steam drum 51 otters many advantages over prior types of boiler steam drums. A primary advantage is inherent in the fact that with the full circle structure dead end pressures are removed and it is unnecessary to provide drum heads at the opposite ends of the drums. Since these drum heads are not necessary, the fabricating cost is reduced and in addition, the strength of the steam header is increased.

During operation, the water and water vapor introduced into the steam drum 51 is continuously passed therethrough into a plurality of vertically extending external supply conduits 81 that are connected at their lower ends to the side of the water-mud drum 84. From the water-mud drum 84, a plurality of wall tubes 82 extend upwardly for connection with steam drum 51. These Wall tubes 82 are disposed in spaced positions about the interior wall 83 of the steam section S. In fact, where loose fill insulation is used, it is intended that the outer surfaces of the tubes 82 will be in contact with the loose fill insulation 17, to hold such insulation in place. Through the upper portion of the steam section S, the tubes 82 will actually be spaced apart a short distance substantially as shown in Fig. 4. Through this particular section small bridging members 85 may be placed between adjacent water tubes 82 to hold the loose fill insulation 17 in place.

At a position slightly below the burners 39, the wall tubes 82 are bent inwardly toward the center of the opening through the shell 15. A portion of the tubes are continued toward the center and bent backwardly to connect with the water drum 84 in such manner that a rectangular opening is formed above the ash pit 23, the arrangement providing an effective ash directing funnel. This rectangular pattern for the tubes 82 is best shown in Fig. 7. In this figure and in Fig. 2, it will be seen that others of the wall tubes 82 are bent downwardly to connect with the top surface of the water drum 84.

Since the water drum 84 is at the lowest point in the circulatory system of this steam generator G it will also act as a mud-drum for the piping system utilized. Accordingly, blow down pipes and valves 26 and 24, previously described, interconnect the combined water-mud drum 84 with the blowdown piping system 25.

Besides the wall tubes 82 that are placed along the interior wall 83 of the steam section S to carry heating medium of low enthalpy, additional screen tubes 82S are provided that pass upwardly and are inclined or bent inwardly through the open center portion of section S. These screen tubes 828 are also connected at their upper end with the steam drum 5]. and at their lower ends with the water drum 84 to receive and carry heating medium of enthalpy greater than that or the heating medium passing through wall tubes 82. In fact these screen tubes 823 form a flash steam generating area.

As shown in Figs. 3 and 4, the screen tubes 828 are cooperatively positioned with respect to the water tubes 32 so that in the upper section as shown in Fig. 4, the screen tubes 825 are aligned with the spaces between the wall tubes 82, whereas in the lower portion of the furnace or boiler as shown in Fig. 3, the screen tubes 828 are bent back into contact with the interior wall 83, so that the walls of the wall tubes 82 and the screen tubes 828 are in contact with each other. This placement of the tubes makes any bridging member unnecessary. Accordingly, even loose fill insulation 17 can be placed behind the tubes 82 in this lower section without danger of escape into the burners.

It will be noted that the hot combustion gases rising through the cylindrical free combustion zone enter a truncated cone-shaped zone formed by the inclined tubes and must pass in part diagonally of the screen tubes toward the superheater tubes. These diagonally-flowing gases then pass upwardly along the upper portions of the superheater tubes and across the outwardly and radially extending ends of the screen tubes; these ends of the screen tubes serve as the flash steam generating area referred to above.

With the circuit arrangement of tubes and conduits described the direction of flow through the tubes is positively controlled. The main circuit and current flow will be downwardly through conduits 81 and upwardly through tubes 82. This pattern assures a uniform liquid level in drum 51 while eliminating longitudinal flow through said drum.

A wide range of boiler sizes is possible with the present design due to the fact that the diameter of the shell 15 may be changed to accommodate a greater number of tubes of the same length, or where desirable the diameter of the tubes themselves may be changed to increase the heat exchange area of the boiler. In general for any particular length of steam producing section S, the diameter of the tubes should be about the same. Only when it is necessary to go to a much increased capacity will it be necessary to change to a larger tube size. Since the tubes used for a considerable number of installations will be of the same size and shape, the fabricating problems coincident with use of a boiler made in accordance with this invention would be considerably less than the fabricating problems of similar present day boiler installations.

Superheaters In order to obtain the temperature and pressure desired for the steam that is to be supplied to the turbine, a plurality of superheater headers as shown in Figs. 2, 5 and 6 are provided. These headers 86 extend from the top of the steam drum 51 outwardly toward the center of the steam section S. Adjacent to the outer ends of the headers 86, a plurality of superheat tubes 87 are connected. These superheat tubes 87 extend vertically through the central opening in section S in positions that are effectively screened from the hottest portion of the furnace gases by the screen tubes 82S adjacent and in front of the tubes 87. Accordingly, insofar as possible burning of the superheat tubes 87 is avoided. At their lower ends the superheat tubes 87 are connected to an outlet header 88. These outlet headers 88 pass outwardly through the shell 15 of section S for connection to a superheat header 89. A large steam trunk 91 is connected to the superheat heater 89 so that superheated steam may be passed directly to the turbine or to other point of use. As shown in Fig. 2, a valve 92 is provided in the steam trunk line 91 so that the flow of superheated steam to the turbine may be controlled at steam generator G. Since the superheat inlet headers 86 are at an elevated position and the outlet headers 88 and super- ;heat drum 89 are at a relatively lower position, the flow m7 of superheat steam through the superheaters 87 is counter current to the directional flow of the hot furnace gases. This counter current flow characteristic insures a more efficient attainment of the elevated temperatures and pressures desired.

A primary advantage of the described type of installation is inherent in the fact that all of the tubes inclusive of superheater tubes 87, wall tubes 82 and screen tubes 825 are relatively longer than the tubes used for comparable purposes in other types of boiler installations. Since they are longer, a fewer number of tubes is needed, thereby reducing installation costs without sacrifice of heat exchange area. Further it should be noted that all of the tubes utilized are relatively straight. This feature makes these tubes easier to install, repair and service while assuring higher efliciency due to the low pressure drop through the straight tubes. In the superheater tubes this is of special importance,since it makes lower pressures in the saturated steam drum ll possible without reduction in line pressure. In fact, with properly placed access doors, it would be possible in this installation to remove single tubes from the circuit without disturbing the operation of adjacent tubes.

if the capacity of the boiler is to be increased, it would be a simple expedient to add additional tubes where necessary. The use of the superheater headers E56 and 88 instead of connecting the superheater tubes 87 directly to the drums 51 and 3% is to facilitate the introduction of additional superheater tubes 87 when desired without having to cut additional holes in the steam drums 51 and 89.

The described structure for the superheater is in itseif especially beneficial inasmuch as there are no low points in the superheater circuit in which water can condense to form passage-obstructing pools. Since there are no points for the entrapment of condensed water during shut down periods, superheaters of the described type may be put back in circuit as soon as steam is initially produced by the tubes of steam section S. This design characteristic which makes it possible to put the boiler and superheaters back on circuit within a relatively short time as compared with present types of boiler installations in itself effects a considerable saving in operating costs.

Where a steam generating unit of this type is to be used with a turbine, the turbine may be placed relatively close to the boiler itself so that only a minimum of connective piping will be necessary.

Summary From the foregoing description and from the drawings, it will be apparent that the present inventor has satisfied a real need in the power plant industry by designing a steam producing installation in which the boiler elements and all boiler auxiliaries are cooperatively designed and coordinated to produce a unitary ductless steam generator of high capacity and efiiciency. Inasmuch as all of the elements are cooperatively designed and positioned, it is unnecessary for the individual power plant designer to undertake the task of coordinating and placing the present day products of separate manufacturers within a proposed power plant set up. To the advantage of all concerned, awkward and cumbersome arrangements of boiler elements are avoided and considerable floor space is saved.

Among the additional features and advantages of the present invention there are several that should be specifically mentioned.

With the cylindrical arrangement of tubes, drums, head ers and boiler shell, the effects of thermal expansion are reduced and avoided. Since most of the boiler elements are arranged in a circular pattern, expansion of the separate elements does not cause relative motion between such element and the other structural members of the installation. The tubes, shell and other elements all cooperatively expand with increases or decreases in operating temperature thereby eliminating the occurrence of expansion stresses. The fact that the turbine can 'be placed closely adjacent to the boiler-stack likewise makes it possible to effect a similar saving since there is no need to make special installations to relieve expansion stresses in the steam lead between the boiler and turbine.

Further, where the drums and headers are installed externally of the boiler shell, these important boiler ele ments are not subjected to the stresses now noted in present installations due to the differential temperature between the inner and outer face of the drums. Since this shearing stress is eliminated, headers and drums of this new design and arrangement will have a relatively longer useful life without requiring reductions in pressure for safety reasons.

With this new design, it is possible to place a greater portion of the boiler elements in the radiant heat zone of the boiler. Accordingly, the boiler tubes, screen tubes, superheater tubes, re-heat tubes, and pro-water heater or ecouomizer can all be placed in the radiant heat Zone of the furnace, thereby increasing production of steam per unit of heat exchange area.

Another advantage is inherent in the fact that since the furnace gases travel upwardly through the center of the steam section S, practically without interruption, there will be no gas pockets formed in the How passages of this installation. With the absence of gas pockets, the need for explosion doors and other similar devices is eliminated. This same structural feature materially reduces draft loss through the boiler so that a relatively high output may be obtained under negative draft conditions. Only under peak power load conditions will it be necessary to use induced draft or force draft fans to increase the output of the installation. Even under peak loads, it will be possible to operate this type of installation without resorting to the high pressures being used in some power plant installations to compensate for the draft loss coincident with the reversed flow characteristics through such installations.

All of the main boiler tubes surfaces in this installation can be cleaned easily with retractable type soot blowers since all of the tubes are located only a short distance from the outside shell surface. The use of long soot blowers is avoided and consequently the prevalence of damaged soot blowers will be minimized.

Due to the cylindrical boiler tube formation all boiler tubes will receive uniform heat so that the water circulation within the tubes will also be uniform thereby causing uniform steam generation around the entire periphery of the circular shaped boiler.

This design is well adapted to unitary construction, and if necessary, a complete unit could be fabricated and moved to an operational site on two or more fiat cars. In cases of emergency this inherent mobility would be a very valuable improvement over prior designs. Further, since oil and condensate storage may be provided as shown in Fig. l, the unitary features of this design are of added importance.

Structurally the present invention has several additional advantages. Besides eliminating the need for separate boiler foundations the new design also eliminates the need for separate foundations and support members for each of the boiler auxiliaries. Further, there is no need for the extensive use of interconnecting conduits and ducts between the boiler elements.

A prime structural advantage is inherent in the fact that essentially this is an outdoor type installation that requires little or no housing. The savings that can be effected through elimination of external housing are considerable and when these savings are combined with other possible economies the cost fi ures for this new type of installation as compared to prior types are impressive. For large installations two or more units may be placed in side by side or otherwise adjacent positions. When this is done an elevator may be conveniently provided for access to the upper components of the installation.

While the installation has been described as cylindrical it is apparent that units may be built that are tapered along the vertical extent of the shell. All such modified structures are specifically included within the term, cylindrical, as used herein.

Besides the advantageous features particularly described and shown, it is likewise apparent that the present invention is adaptable to other modifications and changes of comparable utility. Accordingly, the inventor does not intend to be limited to the embodiment shown but intends only to be limited within the scope of the hereunto appended claims.

What is claimed is:

l. A steam generating power plant comprising an upright shell, burners for the combustion of fuel positioned adjacent the base of said shell to provide a source of heat energy, said shell being effective as a draft stack to induce convection currents of heat energy directed away from said burners and upwardly through said shell, a plurality of tubes in said shell adjacent the walls thereof having heating medium of low enthalpy therein to protect the Walls of said shell from excessive heat, superheater tubes within said shell disposed inwardly from said Walls and first-named tubes at positions exposed to said convection currents of heat energy and to radiant energy from said heat source, screen tubes within said shell having heating medium of intermediate enthalpy therein disposed adjacent to and in front of said superheater tubes for protecting said superheater tubes from excessive temperatures, an upper steam drum connected. in communication with the upper ends of all of said tubes to receive fluid from said first named and screen tubes and to supply fluid to said superheater tubes, a superheat drum connected to the lower ends of said superheater tubes to receive superheated steam therefrom for delivery to a point of use, and means for feeding said heating mediums to the lower ends of said wall tubes and said screen tubes.

2. A steam generating power plant comprising an upright cylindrical shell of uniform cross section, burners for the combustion of fuel positioned adjacent the base of said shell to provide a source of heat energy, said shell being effective as a draft stack to induce convection currents of heat energy directed away from said burners and upwardly through such shell, a plurality of tubes in said shell adjacent the interior walls thereof having heating medium of low enthalpy therein to protect the interior walls of said shell from excessive heat, superheater tubes within said shell disposed inwardly from said walls and first-named tubes at positions exposed to said convection currents of heat energy and to radiant energy from said heat source, screen tubes within said shell having therein heating medium of intermediate enthalpy disposed adjacent to and in front of said superheater tubes for protecting said superheater tubes from excessive temperatures, an upper steam drum connected in communication with the upper ends of all of said tubes to receive fluid from said first named and screen tubes and to supply fluid to said superheater tubes, a superheater drum connected to the outlet end of said superheater tubes for collecting superheated steam that is to be carried to a point of use, and means for feeding said heating mediums to the lower ends of said wall tubes and said screen tubes.

3. A steam generating power plant comprising an up right shell of uniform cross section, burners for the com bustion of fuel positioned adjacent the base of said shell to provide a source of heat energy, said shell being etfective as a draft stack to induce convection currents of heat energy directed away from said burners and upwardly through said shell, a plurality of tubes in said shell adjacent the interior walls thereof having heating medium of low enthalpy therein to protect the walls of said shell from excessive heat, superheater tubes within said shell disposed inwardly from said walls at positions exposed to said convection currents of heat energy and to radiant energy from said heat source, screen tubes within said shell having heating medium of intcrmediatecnthalpy therein disposed adjacent to and in front of said supefheater tubes for protecting said superheater tubes from excessive temperatures, an upper steam drum connected to the upper ends of said first named tubes and said superheater tubes and said screen tubes, a lower superheater drum connected to the outlet ends of said superheater tubes, all of said tubes within said shell being positioned substantially parallel to the direction of flow of said convection currents of heat energy and said superheater tubes being connected to receive steam from said upper drum and to deliver steam to said lower drum so that the flow of heating medium through said superheater tubes is counter current to the direction of flow of said convection currents of heat energy, and means for feeding said heating mediums to the lower ends of said wall tubes and said screen tubes.

4. A steam generating power plant comprising an upright shell of uniform cross section, burners for the combustion of fuel positioned adjacent the base of said shell to provide a source of heat energy, outlet nozzles for said burners positioned to direct the combustion products upwardly through said shell and substantially tangential to the inner surface of said shell, said shell being effective as a draft stack to aid said burners in inducing convection currents of heat energy directed away from said burners and upwardly through said shell in a swirling movement, a plurality of tubes in said shell adjacent the interior walls thereof having heating medium of low enthalpy therein to protect the walls of said shell from excessive heat, superheater tubes within said shell disposed inwardly from said walls and first-named tubes at positions exposed to said convection currents of heat energy and to radiant energy from said heat source, screen tubes within said shell having heating medium of intermediate enthalpy therein disposed adjacent to and in front of said superheater tubes protecting said superheater tubes from excessive temperatures, an upper steam drum connected in communication with the upper ends of all of said tubes to receive fluid from said first named and screen tubes and to supply fluid to said superheater tub es, a superheat drum connected to receive superheated steam from said superheater tubes for delivery to points of use, and means for feeding said heating mediums to the lower ends of said wall tubes and said screen tubes.

5. A steam generating power plant comprising an upright shell of uniform cross section, burners for the combustion of fuel positioned adjacent the base of such shell to provide a source ofheat energy, said shell being effective as a draft stack to induce convection currents of heat energy directed away from said burners and up-- wardly through said shell, an upper steam drum, a lower water drum, an intermediate superheater drum, said drums being spaced vertically from one another, a plurality of tubes within said shell adjacent the wall thereof and having heating medium of low enthalpy therein and connected between said steam and Water drums, headers extending radially from said steam drum and from said superheater drum, a plurality of superheat tubes connecting corresponding vertically spaced pairs of said headers at positions exposed to said convection currents of heat energy and radiant energy from said heat source, screen tubes within said shell connected at the upper ends with said steam drum and at their lower ends with said water drum and having heating medium of intermediate enthalpy therein disposed adjacent to and in front of said superheater tubes protecting said superheater tubes from excessive temperatures, said superheater tubes being interconnected with said headers and drums so that the flow of heating medium through said superheater tubes is counter current to the direction of flow for said convection currents of heat energy, and means for feed ing said heating mediums to the lower ends of said wall tubes and said screen tubes.

6. In a steam generating power plant a unitary combined boiler and stack comprising an upright cylindrical,

hollow frame structure, burners adjacent the lower portions of said hollow structure for introducing fuel and air into the interior thereof for combustion to provide a source of radiant heat energy, said upright cylindrical structure being effective as a draft stack to induce upwardly flowing convection currents of heat energ an upper steam drum of substantially circular form and cross section, an intermediate superheater drum of substantially circular form and cross section, a lower water- 'mud drum of substantially circular cross section, a pinrality of tubes connecting said mud drum and said upper steam drum, said tubes lying closely adjacent one another about the lower portion of the walls of said structure to protect the walls near said burners, and one group of said tubes substantially equally spaced about said Walls being bent inwardly and spaced from the walls above said burners to provide a screen for the remaining ones of said tubes adjacent said wall, and a group of superheater tubes connecting the upper portion of said steam drum and said superheater drum and located between said screen tubes and said remaining tubes for the production of superheated steam.

7. A unitary combined steam boiler and draft stack comprising an upright cylindrical casing, fuel burning equipment in the lower portion of said casing whereby the high flame temperature creates a high draft and the products of combustion rise through said casing, a boiler comprising a water drum near the lowermost portion of said casing and an annular steam drum mounted around the outside of said casing intermediate the ends thereof, boiler tubes within said casing and extending adjacent the inner wall thereof between said drums longitudinally of said casing whereby heat is removed from the products of combustion rising through said casing, an annular superheater drum mounted about the exterior of said casing intermediate said water and steam drums, superheater tubes within said casing extending longitudinally of said casing between said steam drum and said superheater drum and spaced inwardly from the inner walls of said casing for conducting steam to be superheated from said steam drum to said superheater drum in counterfiow to the rising products of combustion, a plurality of screen tubes arranged in front of said superheater tubes and connected between said steam drum and said water drum, and a supporting base for said casing engaging substantially the entire end surface thereof and constituting the entire supporting foundation for the combined boiler and stack.

8. A steam generating plant as set forth in claim 6, wherein said cylindrical structure comprises a continuous metal casing and including thermal insulation about the inner wall of said casing between said first mentioned tubes and said casing, said insulation being retained in position by said tubes and easing.

9. A steam generating plant as set forth in claim 6 wherein the upper ends of said inwardly bent tubes communicate with said upper steam drum above the normal level of liquid therein and the upper ends of the others of said first mentioned tubes communicate with said steam drum below the normal level of liquid therein.

10. A steam generating plant as set forth in claim 6, wherein said water-mud drum is within said structure and is spaced a substantial distance on at least two sides from the inner walls thereof and the lower ends of said first mentioned tubes are bent inwardly toward the center of said structure and form an ash directing funnel at the lower end of said structure.

11. A steam generating plant as set forth in claim 6, wherein said water-mud drum is of rectangular form and is arranged within said structure and is spaced a substantial distance on at least two sides from the inner walls thereof, and the lower ends of said first mentioned tubes being bent inwardly toward the center of said structure to form an ash directing funnel having a rectangular bottom opening, the lower ends of said one group of said 12 first mentioned tubes being connected in communication with said water-mud drum about the inner periphery thereof and the lower ends of the others of said tubes being connected in communication with said water-mud drum about the top thereof.

12. A unitary combined steam boiler and draft stack comprising an upright cylindrical casing, fuel burning equipment in the lower portion of said casing whereby the high flame temperature creates a high draft and the products of combustion rise through said casing, a boiler comprising a water drum near the lowermost portion of said casing and an annular drum mounted around the outside of said casing intermediate the ends thereof, boiler tubes within said casing and extending adjacent the inner walls thereof between said drums longitudinally of said casing whereby heat is removed from the products of combustion rising through said casing, an annular superheater drum mounted about the exterior of said casing intermediate said water and steam drums, superheater tubes within said casing extending longitudinally of said casing between said steam drum and said superheater drum and spaced inwardly from the inner walls of said casing for conducting steam to be superheated from said steam drum to said superheater drum in counterflow to the rising products of combustion, a plurality of said boiler tubes at uniformly spaced intervals about the inner wall of said casing have portions bent inwardly in the portion of said casing between said steam drum and said superheater drum and lying inwardly of said superheater tubes to provide a radiant heat screen for said superheater tubes, said inwardly bent tubes being inclined and their upper ends being nearer the center of said stack than their lower ends, and a supporting base for said casing constituting the entire supporting foundation for the combined boiler and stack.

13. A combined steam boiler and draft stack as set forth in claim 7, wherein said fuel burning equipment comprises burner outlet nozzles positioned to direct the combustion products upwardly through said cylindrical structure and substantially tangential to the inner surface thereof whereby the convection currents of combustion gases are directed upwardly in a swirling movement.

14. A steam generating plant as set forth in claim 4, including a water-mud drum positioned within the base portion of said shell below said burners and spaced from said shell on at least two sides, and wherein the lower ends of said first mentioned tubes and of said screen tubes are bent inwardly toward the center of said shell and are connected in communication with said water-mud drum and form an ash directing funnel at the base of said shell.

15. A steam generating boiler comprising a single upright cylindrical shell, an upper annular steam drum about the exterior of said shell, a water-mud drum within said shell in the base portion thereof, an annular superheat drum about the exterior of said shell between said upper and water-mud drums, means including a plurality of boiler tubes lying in radial planes and spaced uniformly about the inner periphery of said shell for connecting said upper and water-mud drums and shaped to form a free combustion zone having a lower cylindrical portion and an upper truncated cone portion, means including burners positioned about the inner periphery of said shell in the lower portion of said combustion zone for providing a source of radiant heat, and a plurality of superheat tubes connecting said upper drum and said superheater drum, said superheat tubes being uniformly distributed around the annular zone formed between said shell and said boiler tubes adjacent said truncated cone portion of said combustion zone whereby said boiler tubes constitute screen tubes for said superheat tubes and convection gases rising through said truncated cone portion are directed therefrom diagonally of said screen tubes toward said superheat tubes and thence upwardly and out of 13 said annular zone about the upper ends of said boiler tubes extending radially toward said upper drum.

16. A steam generating boiler as set forth in claim 15 ones of said pairs of headers, said rows of tubes lying in planes generally radially of said shell and providing free gas passages therebetween and outlets from said annular zone which are of increasing cross-section outwardly.

mud drum and constitute an ash directing funnel.

18. In a steam generating power plant, a unitary comof hot gases, the lower half 14 said shell being eflfective as a draft stack to induce convection currents of heat energy directed away from said burners and upwardly through said shell, a pluraltubes Within said shell having heating medium of low enthalpy therein, an upper steam drum connected to the upper ends of said tubes, a lower superheater drum, both of said drums being of hollow torus form and positioned externally of said shell for encircling thereabouts, vertically spaced headers extending radial 1y inwardly through said shell from said steam and superheater drums, a plurality of superheater tubes exvertically through the interior of said shell between said spaced headers, a plurality of screen tubes positioned in said shell adjacent to and in front of said superheater tubes having a heating medium of intermediate enthalpy therein and having the upper ends thereof connected to said upper steam drum, and means for feeding said heating mediums to the lower ends of said first mentioned tubes and said screen tubes.

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